1. Field of the Invention
This invention relates to new automotive gasolines having intermediate carbon ranges, and their improved use in internal combustion engines. In particular the invention relates to new gasoline for use in improved gasified carburetion systems.
2. Background Information
Present day automotive gasoline consists of a mixture of hydrocarbons which range from C.sub.4 to about C.sub.12. The lower molecular weight fraction, such as butane isomers, is more volatile and it has always been the practice to include substantial portions of these volatiles in the fuel to insure proper engine performance. This practice, however, is at best a compromise since the presence of the volatiles, on the one hand, causes an undue risk of explosion during storage and handling; and the inherent evaporative end emission losses contribute to pollution; but, on the other hand, the volatiles have always been considered necessary for good cold engine starting. Thus, a certain amount of the volatiles have been incorporated in gasoline. The exact amount of the volatiles may vary according to the climate where it is sold. In fact, industry has set voluntary limits so that each area will have a motor fuel having sufficient volatility for the prevailing climate. High levels of volatile components assure satisfactory starting and warm-up at the lowest temperature expected, and low levels of volatile components protect against vapor-lock in high temperature climates.
Generally current gasolines exhibit high levels of volatiles measured in terms of Reid Vapor Pressure. Reid Vapor Pressure is the accepted measurement of gasoline volatility and it represents the vapor pressure at 100.degree. F. Current fuels require a relatively high amount of volatile components which raises the Reid Vapor Pressure to undesirable levels. It is highly desirable to formulate a fuel which satisfies the volatility requirements without raising the Reid Vapor Pressure to the undesirable level found in the prior art fuels.
The use of these volatiles in prior art fuels is associated with several problems. One such problem is that because present day engines depend on the volatiles, the spontaneous loss of them in storage results in a the fuel which is of inferior quality after a period of storage. Thus, because of varying storage times, the consumer can never be certain if the gas he is purchasing contains the required amount of volatiles at the time of purchase. Naturally, therefore, a fuel whose efficiency and dependability is less dependent on the presence of volatiles is more desirable.
Another problem arising out of the use of these volatiles is the evaporative loss of gasoline which can occur in the gas tank. Industry has been hard pressed to solve this problem for quite some time. While this problem has been recognized for some time, industry has always been reluctant to solve the problem by reducing the volatility of the gasoline because in doing so they would lose the benefits of the compromise (i.e., engine performance). In fact, this point has been expressed in the publication titled Effects of Automotive Emission Requirements on Gasoline Requirements; Symposium, American Society for Testing and Materials; 1971. Here it is stated on page 111 that "Severe volatility reduction could produce other problems. A more effective method than volatility reduction can be seen to be the elimination of evaporative losses by some mechanical device". This invention, however, seeks to reduce volatility or Reid Vapor Pressure and still maintain a fuel which can perform well.
Present day gasoline also contains, in addition to the volatile light-weight and the intermediate-weight components, a heavy-weight component which, like the volatile component, is also associated with several disadvantages. For example, the gasoline of today, when used as a fuel in present day short stroke engines, results in incomplete combustion because there is insufficient time or temperature to burn the heavy hydrocarbon components. This results in a certain amount of gasoline being wasted and this contributes to pollution. Conventional C.sub.4 -C.sub.12 has too much energy in it for conventional internal combustion engines in that if combusted with enough air (stoichiometric or slightly above) it will burn too hot for the engine or it will produce high levels of nitrous oxides. Yet, in spite of these shortcomings, the heavy components are left in present day fuel because their presence is considered necessary to provide a fuel having suitable properties for automotive use.
The presence of these heavy components in conventional C.sub.4 -C.sub.12 gasoline requires considerable front end priming with light components (C.sub.4 and/or C.sub.5) to achieve adequate front end volatility for starting engines equipped with standard carburetion systems. In addition, conventional C.sub.4 -C.sub.12 gasoline which contains these heavy components (C.sub.11 and C.sub.12) cannot be easily gasified and maintained in the gaseous state without recondensing. Consequently, conventional C.sub.4 -C.sub.12 gasoline has limited utility in a more efficient carburetion system of the type which requires gasification in the absence of air before mixing the gasified fuel with air for combustion. Therefore, in view of the shortcomings associated with the heavy weight hydrocarbons, especially C.sub.11 and C.sub.12, it would be highly desirable to formulate the gasoline without these heavy components being present while also avoiding the problems associated with the absence of these components.
The use of conventional C.sub.4 -C.sub.12 fuels in standard carbureted internal combustion engines requires that the volatility of the fuel be adjusted to achieve a Reid Vapor Pressure of at least 9 in the summer and 12 in the winter. If the Reid Vapor Pressure of conventional C.sub.4 -C.sub.12 gasoline falls below the above limits, starting and running the engine is severely impaired. The fuels of the present invention will easily start and operate identical engines yet these fuels have a reduced Reid Vapor Pressure in comparison to the above-mention conventional C.sub.4 -C.sub.12 gasoline. Thus the summer fuels of the present invention may have a Reid Vapor Pressure less than 9 and the winter fuels may have a Reid Vapor Pressure of less than 12. In particular, it is been discovered that the fuel of the present invention having a Reid vapor Pressure as low as 6 in the summer and 9 in the winter will easily start and operate identical engines which require conventional fuels having a Reid Vapor Pressure of 9 in the summer and 12 in the winter. The Reid Vapor Pressures can be reduced even further by using the fuels of the present invention in combination with the improved carburetion system of the present invention.
The ideal combustion mixture for internal combustion engines consists of gasoline in the vapor or gaseous state thoroughly mixed with adequate air to support combustion. In this condition, fuel-rich pockets, which are responsible for detonation or "knock," are eliminated and carbon deposits responsible for preignition are minimized due to more complete combustion. Because detonation or preignition can damage or ruin an engine, current gasolines have octane boosters such as aromatics contained therein to reduce "knock" since current engines have fuel and air intake systems which produce droplets of fuel that contribute to fuel rich pockets in the combustion chambers of the engines. Slowing the burn with octane boosters lowers the combustioncy efficiency of the engine and increases the exhaust pollution. Therefore, it would be highly desirable to provide a fuel which avoids octane boosters, is rated at a lower octane value but which has highly desirable burning characteristics so that the fuel does not produce engine knock.
Automotive and aviation gasolines have always had an ASTM average octane number (.sup.R+M /.sub.2) of 80 or higher; wherein R represents the research octane number and M represents the motor octane number. Current engines generally require an average octane number in excess of 85.